Going straight into a PhD without a Masters is more common in the Sciences than Humanities, certainly. Appropriate professional experience might help if it's directly related to your proposed research, but your biggest problem will be the lack of an academic research track record. It's not really so much about study at PhD level, more about your ability to take primary material and formulate new/innovative ways of interpreting or re-interpreting it. A Masters would give you that background. Plus in the Sciences, much PhD-level research is collaborative, so a track record in group research would be an additional advantage.
There's very little funding available for Masters courses anyway, so I doubt doing the PGCE will disadvantage you hugely. The funding that exists for that level is insanely competitive and very difficult to win - although again, the Sciences are marginally better funded than Humanities (just don't bank on that being the case in ten years' time). There's no equivalent of the undergrad student loan/grant system. From my own experience and that of my colleagues, Masters courses are usually funded from personal savings, commercial loans (although even Career Development Loans are becoming more difficult to access) or indulgent relatives.